Lignosulfonates carboxylated with carbon dioxide as additives in oil recovery processes involving chemical recovery agents

ABSTRACT

A process for producing petroleum from subterranean formations is disclosed wherein production from the formation is obtained by driving a fluid from an injection well to a production well. The process involves injecting via the injection well into the formation an aqueous solution of lignosulfonate salt carboxylated with carbon dioxide as a sacrificial agent to inhibit the deposition of surfactant and/or polymer on the reservoir matrix. The process may best be carried out by injecting the lignosulfonates carboxylated with carbon dioxide into the formation through the injection well mixed with either a polymer, a surfactant solution and/or a micellar dispersion. This mixture would then be followed by a drive fluid such as water to push the chemicals to the production well.

This application is a continuation-in-part of co-pending applications, Ser. No. 900,691 filed Apr. 27, 1978, now abandoned, Ser. No. 745,505, filed Nov. 26, 1976 and Ser. No. 715,957, filed Aug. 19, 1976, both now abandoned and application Ser. No. 591,573, filed June 30, 1975, now abandoned and co-pending application Ser. No. 591,574 filed June 30, 1975, now U.S. Pat. No. 4,006,779.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the recovery of oil from subterranean formations by chemical flooding methods.

2. Description of the Prior Art

Petroleum is frequently recovered from subterranean formations or reservoirs by permitting the natural energy of the reservoir to push the petroleum up through wells to the surface of the earth. These processes are referred to as primary recovery methods since they use the natural energy of the reservoir. However, a large amount of oil, generally in the range of 65-90% or more, is left in the subterranean formation at the conclusion of the primary recovery program. When the natural reservoir energy is unable to produce more petroleum, it is a common practice to resort to some form of supplemental recovery technique in order to recover additional petroleum left in the subterranean formation. These supplemental operations are normally referred to as secondary recovery operations. If this supplemental recovery operation is the second in a series of such operations, it will be referred to as a tertiary recovery operation. However, the terminology is unimportant for the purposes of this application and relates only to the sequence in which they are carried out.

The most widely used supplemental recovery technique because of its ease of implementation and low capital outlay is water flooding through injection wells drilled into the subterranean formation. In a water flooding operation, the injected fluid displaces oil through the formation to be produced from the injection well. A major disadvantage to water flooding, however, is its relatively poor displacement efficiency largely due to the fact that water and oil are immiscible at reservoir conditions and high interfacial tension exists between the flood water and the oil. For this reason, after a water flood, a large portion of the oil is still left unrecovered in the reservoir.

It has been recognized by those skilled in the art that a solution effecting a reduction in this interfacial tension between water and oil would provide a much more efficient recovery mechanism. Therefore, the inclusion of a surface active agent or surfactant in the flood water was recognized as an acceptable technique for promoting displacement efficiency of the reservoir oil by the water. For example, U.S. Pat. No. 3,468,377 discloses the use of petroleum sulfonates in water flooding operations and U.S. Pat. No. 3,553,130 discloses the use of ethylene oxide adducts of alkyl phenols for the same purpose. The use in water flooding operations of water soluble surface active alkaline earth resistant polyglycol ethers is disclosed in U.S. Pat. No. 2,233,381. Other specialized surfactants, as will be discussed later, have been discovered to have special properties useful in water flooding operations such as a tolerance for high salinity and calcium, and/or magnesium ion concentrations often found in reservoir waters.

However, field operations employing surfactants and surface active agents in injected fluid have not always been entirely satisfactory due to the fact that these materials are often absorbed by the formation rock to a relatively high degree, resulting in an ever declining concentration of the materials as they progress through the reservoir. Therefore, large concentrations of surface active materials have heretofore been necessary to maintain a sufficient concentration at the oil-water interface. Due to this, many proposed flooding operations involving surface active materials have been uneconomical.

Another serious problem for any recovery technique involving the driving of oil with a fluid is premature breakthrough of the injection fluid. This premature breakthrough indicates that the reservoir has not been adequately swept of oil. The problem is often described in terms of sweep efficiency as distinguished from the displacement efficiency described above. Displacement efficiency involves a microscopic pore by pore efficiency by which water displaces oil, whereas sweep efficiency is related to the growth portion of the reservoir which is swept and unswept by the injected fluid. A major cause of poor sweep efficiency is associated with the fact that the injected fluid generally has a lower viscosity than the displaced fluid (petroleum). Thus, the injected fluid has a higher mobility and tends to finger through the oil, prematurely breaking through to the production well.

One solution to this high mobility problem is to increase the viscosity of the driving fluid. A way to do this is to add polymeric organic materials to a driving water which has the effect of increasing the viscosity of the water, thereby increasing the sweep efficiency of the supplemental recovery process. U.S. Pat. No. 3,039,529 and U.S. Pat. No. 3,282,337 teach the use of aqueous polyacrylamide solutions to increase the viscosity of the injected fluid thereby promoting increase sweep efficiency. Polysaccharides as taught in U.S. Pat. No. 3,581,824 have been used for the same purpose. These polymers are quite expensive and any polymer lost to adsorption on the reservoir matrix adds substantially to the cost since additional polymer is required to maintain a given viscosity.

The above described problems have been recognized by those skilled in the art of oil recovery and certain sacrificial compounds have been added to pretreat the formation in order to decrease the adsorption of subsequently injected surfactants and/or polymers. For example, U.S. Pat. Nos. 3,424,054 discloses the use of aqueous solutions of pyridine; U.S. 3,469,630 discloses the use of sodium carbonate and inorganic polyphosphates and U.S. 3,437,141 discloses the use of sodium carbonates, inorganic polyphosphates and sodium borate in combination with saline solution of a surfactant having both a high and a low molecular weight component. These materials have not been completely satisfactory from a standpoint of performance and economics however.

U.S. Pat. No. 3,384,171 to Parker discloses that unmodified lignosulfonates may be used as a preflush followed by a surfactant solution. While this method provides an improvement over using surfactant alone, my invention provides an improvement in oil recovery over the process of Parker. My copending application Ser. No. 715,957 filed Aug. 19, 1976 claims unmodified lignosulfonates as sacrificial agents. The present invention provides an improvement over that process.

SUMMARY OF THE INVENTION

The invention is a process of producing petroleum from subterranean formation having an injection well and a production well in communication therewith. The process comprises injecting into the formation via the injection well an aqueous solution of lignosulfonate salts carboxylated with carbon dioxide in admixture with a chemical oil recovery agent, for example, surfactant, polymer and/or a micellar dispersion. It is the usual practice to then inject a fluid such as water to sweep the chemical components through the reservoir to the production well, thereby displacing oil from the subterranean formation to the surface of the earth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A sacrificial material is injected by the process of this invention through an injection means comprising one or more injection wells into a subterranean petroleum-containing formation to preferably occupy or cover all potential adsorption sites of the rock within the subterranean formation thereby reducing the extent of adsorption of the more expensive chemical oil recovery agent injected therewith. A sacrificial agent performs best when it exhibits high adsorption on active sites of rock surfaces, and thus diminishes surfactant and/or polymer adsorption. Chemical compounds of polyelectrolytic nature have the proper physico chemical and structural requirements to behave as successful sacrificial agents. The functional group on the sacrificial agent molecules enhances adsorption either by hydrogen bonding or electrostatic attraction to active sites on the rock surfaces.

A satisfactory sacrificial material has at least three important characteristics. First, it should be less expensive than the surfactant on a cost effectiveness basis since it is to be sacrificed or adsorbed by the formation, probably not to be recovered. Next, it must be adsorbed readily by the subterranean formation matrix. Preferably the sacrificial material should be adsorbed more readily than the chemical oil recovery agent to be used in the process. The third important characteristic of a sacrificial agent is that the presence of such adsorbed sacrificial material should retard or eliminate adsorption of the surfactant and/or polymer chemical recovery material on the adsorption sites of the formation rock. By adsorption sites of the formation rock it is meant those parts of the surfaces of the pores of the formation rock capable of adsorbing a chemical compound from a solution on contact.

The sacrificial material may not have a detrimental effect on the recovery efficiency of the chemical flooding operation. Additional oil is usually recovered only if the sacrificial material is followed by or is admixed with a surfactant and/or a polymer chemical recovery agent which will effectively increase the amount of oil displaced from the subterranean formation. When the surfactant is chosen as the chemical recovery agent it should be injected in admixture with the sacrificial agent for best results and ahead of the following flooding water thereby achieving the desired interfacial tension reduction between the injected fluid and the displaced fluid with minimal loss of surfactant on the formation matrix. The surfactant may be present in a hydrocarbon solvent or in an aqueous solution or in a combination thereof. Any anionic, nonionic and/or cationic type of surfactant known in the art may be used in the practice of this invention. Some types of surfactants were mentioned previously. In addition, surfactants disclosed and claimed in the following U.S. Patents, for example, are particularly useful since they have been found to be capable of performing in reservoirs having both high salinities and high hardness levels: U.S. Pat. Nos. 3,858,676; 3,811,505; 3,811,504 and 3,801,507.

Likewise, the amount of surfactant which must be employed in the practice of any chemical flood is generally known in the art and is to be found in published literature. However, the slug size of surfactant generally will range from about 0.01 to 1 pore volumes of an aqueous surfactant solution having dissolved therein from about 0.01 to about 10.0 percent by weight of the surfactant itself.

In my invention the sacrificial agent is preferably injected in admixture with the surfactant slug into the petroleum formation. This surfactant/sacrificial agent mixture may or may not be preceded by a slug of sacrificial material in aqueous solution only. It has been found that this technique is superior to the preflush method of injecting a slug of sacrificial material followed by a slug of surfactant solution without sacrificial material. However, the preflush method is superior to using no sacrificial material at all.

In any of these embodiments and others which are obvious to those skilled in the art, the surfactant containing slug may be followed by a material to taper the viscosity before drive water is injected. This technique known well to those skilled in the art prevents the water from fingering into the more viscous surfactant containing slug.

In a specific embodiment of this invention, a sacrificial material comprising lignosulfonate salts carboxylated with carbon dioxide, is injected via the suitable injection means, i.e. through one or more injection wells completed in the subterranean hydrocarbon formation, in admixture with a surfactant solution. By injecting the sacrificial material and surfactant together oil recovery is maximized. The oil recovery is greater than preflushing the formation with sacrificial agent and followed with surfactant solution.

Another embodiment of my invention is the use of modified lignosulfonates in conjunction with an emulsion of water, hydrocarbon and surfactant, i.e. a micellar dispersion. The same parameters as discussed above for simple aqueous surfactant solutions would apply to micellar dispersions. Micellar dispersions are known in the art. See for example, U.S. Pat. No. 3,536,136 incorporated here by reference.

The sacrificial agents useful in the process of my invention are lignosulfonate salts carboxylated with carbon dioxide. Lignosulfonates are anionic polyelectrolytes soluble in water and tolerate hard water (polyvalent ions, e.g. calcium and magnesium). They are also thermally stable in formations where the temperature is high. Lignosulfonates are macromolecules built up by comlex condensation of phenyl propane units. The sulfonate groups are attached to the aliphatic side chain, mainly to alpha carbon. Lignosulfonates are water soluble with molecular weights ranging from several thousand to around 50,000 or more. They are economically attractive since being by-products of the pulping industry, they are plentiful and cost less than either the surfactants or the polymers used in enhanced oil recovery methods. The polyelectrolyte lignosulfonates with strongly ionized sulfonate groups are negatively charged species and have a tendency to absorb on solid surfaces thereby imparting a negative charge to them. The rock surfaces of a reservoir treated with lignosulfonate will be inert towards the anionic surfactants in the flood water and therefore loss of surfactants to the rock surfaces will be kept to a minimum. The same phenomenon will occur with the polymer thickened drive fluid.

Lignin is second only to cellulose as the principal constituent in wood. Generally, lignin is a complex phenolic polyether containing many different functional groups including carboxyls, carbonyls and alcoholic and phenolic hydroxyls. Lignins and their derivatives are described in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Vol. 12, beginning at page 362. This publication describes two very broad classes of lignin derivatives: sulfite lignins and alkali lignins.

The difference in the lignins exists because of the method of extraction of lignin material from woody materials. Sulfonated alkali lignins are readily available commercially from various sources including but not limited to West Virginia Pulp and Paper Company under the trade name REAX. Their general method of preparation is described in the Encyclopedia of Chemical Tehnology referred to above. Briefly, sulfonated alkali lignins are prepared by cooking woodchips with a 10% solution of a mixture of sodium hydroxide with about 20 mole percent of sodium sulfide. The lignin with wood is modified into a sodium compound often termed sodium lignate or alkali lignin which is very soluble in the strongly alkaline solution. These alkali lignins are removed from solution by lowering the pH which precipitates out the alkali lignins. These unsulfonated alkali lignins are sold under various tradenames including INDULIN. These alkali lignins are used to prepare the sulfonated derivatives. Methods of sulfonation are known by those skilled in the art. One typical method involves treating the alkali lignins with a solution of alkali sulfites at elevated temperature and pressure. The degree of sulfonation may be controlled to provide a variety of sulfonated alkali lignins.

The other main type of lignin derivatives are called sulfite lignins or sulfite lignosulfonates. Sulfite lignins are generally made by cooking woodchips under pressure in a solution of sulfurous acid and calcium, magnesium, sodium or ammonium bisulfite. This process converts insoluble lignins to soluble lignosulfonic acid. The lignosulfonic acids or calcium, magnesium, sodium or ammonium salts of the lignosulfonic acids are available under various tradenames including MARASPERSE, LIGNOSITE, ORZAN, TORANIL, and RAYFLO.

The broad term lignosulfonates used herein refers to both sulfonated alkali lignins and sulfite lignosulfonates (sulfite lignins). These are distinct types of compounds as explained above. Since the alkali lignins require sulfonation after extraction of the material from woody products it is proper to call them sulfonated alkali lignins. Likewise since sulfite lignins emerge from the extraction process already sulfonated it is proper to refer to this class of materials as sulfite lignins or sulfite lignosulfonates.

My invention is the use of sulfonated alkali lignins and sulfite lignosulfonates, each modified by carboxylation with carbon dioxide. Lignosulfonates having degrees of sulfonation from about 2.0 to saturation are acceptable as starting materials for the modified lignosulfonates of my invention. Cations which are acceptable include Na⁺, K⁺, NH₄ ⁺, Ca⁺⁺, and Mg⁺⁺. The degree of sulfonation is the weight percentage of sulfonate (SO₃ ⁻) compared to the total molecular weight.

Crude unmodified lignosulfonates may be made with either softwoods or hardwoods. Although having basically the same functional groups the crude unmodified softwood lignosulfonates have more sulfonate and hydroxyl groups than the crude unmodified hardwood lignosulfonates. Thus, in general, crude unmodified softwood lignosulfonates have better hard water (Ca⁺⁺, Mg⁺⁺) tolerance than the hardwood form.

Carbon dioxide reacts predominantly with the ortho sites of the aryl groups in the lignosulfonate molecule and to a lesser extent with the para sites. This is well known in the art as the Kolbe reaction.

Carbon dioxide carboxylated lignosulfonates may be prepared by the direct addition of carbon dioxide on a lignosulfonate salt or the addition of a salt such as sodium bicarbonate which liberates carbon dioxide and thus carboxylates the lignosulfonate. In the first method, a lignosulfonate salt is treated with a strong base such as sodium hydroxide and then carbon dioxide is contacted with the alkali lignosulfonate at elevated temperatures and pressures. The pressure may be from about 5 to about 50 atm and the temperature from about 100° to 300° C. A digesting time sufficient to react the carbon dioxide and lignosulfonate at the chosen conditions is used. During the digestion period, the pressure may rise. After the reaction is complete, the contents are cooled and the carboxylated lignosulfonate is neutralized with an acid such as dilute hydrochloric acid. An alternate way of carboxylating lignosulfonates with carbon dioxide involves treating the lignosulfonate salt with a strong base such as sodium hydroxide and then contacting the alkali lignosulfonate with a salt such as sodium bicarbonate under similar temperature and pressure conditions as the direct contact of carbon dioxide above. In this alternative method, the sodium bicarbonate releases carbon dioxide which reacts with the lignosulfonate salt and carboxylates it. After the reaction is complete, the carboxylated lignosulfonate salt is neutralized in the presence of a dilute solution of an acid such as hydrochloric acid. The presence of CO₂ H groups in the carboxylated lignosulfonates may be confirmed by analytical techniques such as infrared spectroscopy.

Other routes to carboxylating lignosulfonates may be apparent to those skilled in the art and this disclosure of suggested methods is not intended to limit the invention.

The quantity of lignosulfonates carboxylated with carbon dioxide to be injected into the subterranean hydrocarbon formation may be any amount up to and including an amount sufficient to occupy substantially all of the active sites of the formation matrix. If less than the maximum amount is used, there will be a corresponding increase in the adsorption of surfactant from injection solution onto the formation matrix although the amount of increase will not be as great as in the case where the formation is completely free of lignosulfonate salts carboxylated with carbon dioxide. At a maximum, only the amount of modified lignosulfonate salts needed to completely occupy the active sites on the formation matrix is needed. The detriment resulting from using excess modified lignosulfonate salts would be an increase in the cost of operating the oil recovery program.

The amount of lignosulfonate salts carboxylated with carbon dioxide needed in the process of the invention depends on the particular formation, the area or pattern to be swept and other formation characteristics. Those skilled in the art can determine the exact quantity needed to afford the desired amount of protection.

Generally it has been found that the amount of lignosulfonate carboxylated with carbon dioxide in the surfactant slug will be effective in amounts of from about 0.01 to about 10.0 percent by weight of the total surfactant solution (including the aqueous portion). Total lignosulfonate carboxylated with carbon dioxide will be effective at the above concentrations in amounts ranging from 0.01 to 1.0 pore volumes of the aqueous solution of surfactant-sacrificial agent or only sacrificial agent solution.

The effectiveness of this invention for reducing the adsorption of surfactant or polymer on formation rock and chemical flooding operations is demonstrated by the following examples which are presented by way of illustration and are not intended as limiting the spirit and scope of the invention as defined in the claims.

The following Examples demonstrate the preformance of modified lignosulfonates in oil recovery from crushed limestone packs or sand packs in the laboratory.

EXAMPLE I Preparation of Lignosulfonates Carboxylated with Carbon Dioxide

106 grams of lignosulfonate is treated with 500 ml of 1.5 N NaOH. A portion of the alkaline lignosulfonate solution (45 g of solids) is carboxylated by stirring the solution (pH is greater than or equal to 10) with 10 g NaHCO₃ in 400 ml H₂ O in an autoclave at 170° C. for 5 hours at 25 atmospheres pressure. The carboxylated lignosulfonate produced is acidified with 10% HCl and the product is filtered. The presence of --CO₂ H groups in the carboxylated lignosulfonates is confirmed by IR spectroscopy.

A shake bottle test is performed using the above prepared lignosulfonates to test the mitigation of surfactant adsorption on CaCO₃. A sulfonated 4 mole ethylene oxide adduct of dodecyl phenol is the surfactant. The test demonstrates that the presence of the lignosulfonate reduces the amount of surfactant adsorption on the CaCO₃.

EXAMPLE II

The starting crude lignosulfonates were either hardwood of softwood products. The calcium salt was converted to sodium salt to evaluate the effect of this modification step. Lignosulfonates were modified by performing reactions such as carboxylation by oxidation, carboxylation by chloroacetic acid, sulfomethylation and carboxylation by reaction with carbon dioxide. Each reaction yields products with different functional groups. The types of functional groups obtained by each reaction are additive and those affect both the tolerance of lignosulfonates to brine and the affinity of lignosulfonates to adsorb on surfaces of interest. The choice of an adsorbent to be used in the evaluation of sacrificial agents is important. For accurate evaluation, one must utilize adsorbents which allow high surfactant adsorption.

To compare the effectiveness of various lignosulfonates as sacrificial agents the single surfactant system sulfonated four mole ethylene oxide adduct of dodecyl phenol was used. Shake bottle tests were performed to evaluate the mitigation of surfactant adsorption to precipitated CaCO.sub. 3 at 77 kg/m³ TDS and 43° C. Adsorption values of Adduct D-40 CS* with or without lignosulfonates present are tabulated below:

    __________________________________________________________________________     Surfactant System                                                              10 kg/m.sup.3 Adduct D-40CS           mg Surfactant Adsorbed                   + 10 kg/m.sup.3 Lignosulfonate                                                               Description             g CaCO.sub.3                             __________________________________________________________________________     No Lignosulfonate                     22.8                                     Norlig 42Z    Na salt; Hardwood; Carboxylated by Oxidation                                                           6.5                                      Norlig 42CAA  Na salt; Hardwood, Carboxylated by                                             Chloroacetic acid       12.0                                     Norlig 42ZCAA Na salt; Hardwood, Carboxylated by Oxidation                                   and Chloroacetic acid   5.0                                      Norlig 92Z    Na salt; Softwood, Carboxylated by Oxidation                                                           1.0                                      Norlig 92CAA  Na salt; Softwood, Carboxylated by                                             Chloroacetic acid       9.7                                      Norlig 92ZCAA Na salt; Softwood, Carboxylated by Oxidation                                   and Chloroacetic acid   0.5                                      Norlig 41ZCAA Ca salt; Hardwood, Carboxylated by Oxidation                                   and Chloroacetic acid   10.4                                     Norlig 91ZCAA Ca salt; Softwood, Carboxylated by Oxidation                                   and Chloroacetic acid   1.0                                      Norlig 51 S-Z Ca salt; Softwood, Sulfomethylated, Carboxylated                               by Oxidation            4.1                                      __________________________________________________________________________

Results indicate that the softwood lignosulfonate derivatives exhibit greater mitigation of surfactant adsorption than the hardwood lignosulfonate derivatives when CaCO₃ is used as adsorbent. Conversion from Ca salt to Na salt has a moderate beneficial effect on the effectiveness of the product. Improved tertiary oil recovery efficiency achieved when lignosulfonates are incorporated into surfactant systems may not be solely due to a sacrificial agent effect. In addition to mitigation of surfactant adsorption on pore surfaces, other mechanisms may also contribute to an improved oil recovery efficiency of a surfactant system.

EXAMPLE III

Modified lignosulfonates exhibit high sacrificial agent activity when exposed to calcium carbonate surfaces in shake bottle tests. Several different reaction have been employed to obtain derivatives of lignosulfonates. Four are:

(A) Oxidation reaction

(B) Chloroacetic acid reaction

(C) Sulfomethylation reaction, and

(D) Carbon dioxide reaction.

Modified lignosulfonates with several types of functional groups can be prepared by employing any one of the above reactions or combinations of these reactions. The availability of modified lignosulfonates with different types of functional groups is desirable because the more functional groups lignosulfonates have, the greater tolerance to higher salinity and hardness brines. The presence of different types of functional groups (both polar and nonpolar) on lignosulfonates should contribute to the attractive forces on substrates and enhance the sacrificial agent activity of these compounds.

The surfactant system (as in Example II) (with or without lignosulfonates) was used to determine relative sacrificial agent effectiveness of lignosulfonates on precipitated calcium carbonate. Shake bottle tests were performed to evaluate surfactant adsorption mitigation at 77 kg/m³ TDS and 43° C. Several adsorption values of Adduct D-40CS with or without lignosulfonates present are tabulated below:

    ______________________________________                                         Surfactant System                                                              10 kg/m.sup.3 Adduct D-40CS                                                                              mg Surfactant                                        +                         Adsorbed                                             10 kg/m.sup.3 Lignosulfonate                                                                             g CaCO.sub.3                                         ______________________________________                                         No sacrificial agent      21.6                                                 Norlig 92g (Softwood: unmodified, Na salt)                                                               17.5                                                 Norlig 92Z (Softwood: oxidized, Na salt)                                                                 1.0                                                  Norlig 41ZCAA*                                                                 (Hardwood: oxidized, carboxylated, Ca salt)                                                              10.4                                                 Norlig 41SCAA                                                                  (Hardwood: sulfomethylated, carboxylated,                                      Ca salt)                  11.3                                                 Norlig 91ZCAA                                                                  (Softwood: oxidized, carboxylated Ca salt)                                                               1.0                                                  Norlig 91SCAA                                                                  (Softwood: sulfomethylated, carboxylated Ca salt)                                                        6.0                                                  ______________________________________                                          *All products with "CAA" in the name were carboxylated with chloroacetic       acid.                                                                    

It is observed that the oxidized and carboxylated lignosulfonates are more effective sacrificial agents here than the sulfomethylated and carboxylated ones. This is true for both the hardwood and softwood derivatives. It is to be noted that the softwood modified lignosulfonates exhibit greater surfactant adsorption inhibition on CaCO₃ than the hardwood modified lignosulfonates. This is probably due to the fact that the softwood degree of sulfonation is higher than the hardwood degree of sulfonation.

Since various structural forms of modified lignosulfonates are available, it is possible to prepare modified lignosulfonates which should exhibit high surfactant adsorption mitigation for a given surfactant system on a substrate of interest such as limestone, sandstone and others.

EXAMPLE IV

Derivatives of lignosulfonates exhibit varying degrees of sacrificial agent activity when calcium carbonate is used as substrate. Oxidized and carboxylated lignosulfonates have been tested for surfactant adsorption mitigation. In this investigation sandstone (Dog Lake EE sand) was used to determine how structural differences of modified lignosulfonates affect their performance as sacrificial agents on sandstone.

The surfactant (as in Examples I and II) was used in surfactant systems where the salinity was maintained at 77 kg/m³ TDS and the temperature at 43° C. Quantities of 50 of sandstone were exposed to 50 cc surfactant solutions to achieve large enough surfactant concentration changes for accurate adsorption value determinations. Bottles containing the mixtures were shaken for 24 hours and then they were equilibrated for 3 days prior to centrifugation, which was done to effectively separate the adsorbent from the equilibrium solutions. Several adsorption values of systems composed of 10 kg/m³ (1%, w/v) surfactant and 10 Kg/m³ (1%, w/v) lignosulfonate are tabulated below:

    ______________________________________                                                               mg                                                                             Surfactant Adsorbed                                      Lignosulfonates       g Dog Lake EE Sand                                       ______________________________________                                         No sacrificial agent  1.5                                                      Norlig 92g (Softwood: unmodified)                                                                    1.1                                                      Norlig 92Z (Softwood: oxidized Na salt)                                                              0.8                                                      Norlig 92ZCAA (Softwood: oxidized,                                             carboxylated, Na salt)                                                                               0.7                                                      Norlig 42Z (Hardwood: oxidized, Na salt)                                                             0.5                                                      Norlig 42ZCAA (Hardwood: oxidized,                                             carboxylated, Na salt)                                                                               0.4                                                      ______________________________________                                    

The adsorption tests indicated that both the oxidized and the oxidized and carboxylated lignosulfonates have greater effectiveness as sacrificial agents on sandstone substrates than the unmodified lignosulfonate. Results also indicate that both the oxidized and the oxidized and carboxylated hardwood lignosulfonates are more effective than the corresponding softwood lignosulfonates as sacrificial agents where sandstone is used as adsorbent. For CaCO₃ as adsorbent oxidized or oxidized and carboxylated softwood lignosulfonates were more effective sacrificial agents than oxidized or oxidized and carboxylated hardwood lignosulfonates.

The differences in performance between the hardwood and softwood derivatives can possible be explained on the basis of their chemical structures. Softwood lignosulfonates are predominantly of the quaiacyl structure, whereas hardwood lignosulfonates have both the quaiacyl and the syringyl structures. The major feature of the oxidation reaction is the conversion of methoxyl groups (inactive) to phenolic groups (active). Thus, oxidized hardwood lignosulfonates have more phenolic groups because the syringyl structure has twice as many methoxyl groups than the quaiacyl structure. Hydrogen bonding between the phenolic groups of the oxidized lignosulfonates and the oxygens of the sandstone surfaces is probable mechanism contributing to the enhanced adsorption of oxidized lignosulfonates on sandstone. It should be emphasized that electrostatic attraction between the anionic functional groups (sulfonates and carboxylates) on the modified lignosulfonates and sandstone surfaces also contributes to the adsorption of these lignosulfonates.

The following examples (V-IX) demonstrate the performance of modified lignosulfonates in oil recovery from crushed limestone packs or sand packs in the laboratory. In those tests the packs were saturated with oil and then water flooded to a residual oil saturation. Then the surfactant solutions were injected followed by polymer solutions.

EXAMPLE V

    ______________________________________                                         OIL RECOVERY FROM CRUSHED LIMESTONE PACKS                                      ______________________________________                                         Surfactant                                                                             0.4% Dodecylbenzene sulfonate + 0.6%                                   System: Sulfonated 4 mole $O adduct of nonyl phenol                                    + 1.0% Lignosulfonate in 65,000 ppm TDS brine                          Polymer:                                                                               0.1% Polysaccharide polymer B-1459 in                                          65,000 ppm TDS brine                                                   ______________________________________                                                      % Pore    % Pore                                                  Sulfomethy-  Volume    Volume     % Tertiary                                   lated Ligno- Surfactant                                                                               Polymer    Oil                                          sulfonates   Injected  Injected   Recovery                                     ______________________________________                                         None         20        50         62.8                                         Marasperse BS-22-3                                                             (Sulfomethylated                                                               Na salt)     20        50         91.0                                         Marasperse 22 S-Z                                                              (sulfomethylated                                                               and oxidized Na salt)                                                                       20        50         88.6                                         ______________________________________                                    

EXAMPLE VI

    ______________________________________                                         Surfactant                                                                             1% Sulfated 4 mole EO adduct of nonyl phenol                           System: + 1% Lignosulfonate in 180,000 ppm TDS brine                           Polymer:                                                                               0.1% Polysaccharide polymer B-1459 in                                          180,000 ppm TDS brine                                                  ______________________________________                                                      % Pore    % Pore                                                  Sulfomethy-  Volume    Volume     % Tertiary                                   lated Ligno- Surfactant                                                                               Polymer    Oil                                          sulfonates   Injected  Injected   Recovery                                     ______________________________________                                         None         15        50         60.0                                         Marasperse BS-22-6                                                             (sulfomethylated                                                               Na salt)     15        50         76.7                                         Marasperse 22S-Z                                                               (Sulfomethylated and                                                           oxidized Na salt)                                                                           15        50         79.4                                         Norlig 41S-2Z                                                                  (sulfomethylated and                                                           oxidized Ca salt)                                                                           15        50         78.0                                         ______________________________________                                    

EXAMPLE VII

    ______________________________________                                         OIL RECOVERY FROM DOG LAKE SAND PACKS                                          ______________________________________                                         Surfactant                                                                             2.0% Petroleum sulfonate                                               System: + 0.6% sulfonated 6 mole EO adduct nonyl                                       phenol                                                                         + 1% Lignosulfonate in 105,000 ppm TDS brine                           Polymer:                                                                               0.1% Polysaccharide polymer B-1459                                     ______________________________________                                         Sulfomethy-  % Pore    % Pore                                                  lated and    Volume    Volume     % Tertiary                                   Carboxylated Surfactant                                                                               Polymer    Oil                                          Lignosulfonate                                                                              Injected  Injected   Recovery                                     ______________________________________                                         None         25        100        65.8                                         Norlig 42SCAA                                                                               25        100        82.1                                         Na salt, hardwood                                                              sulfomethylated then                                                           reacted with chloro-                                                           acetic acid                                                                    ______________________________________                                    

EXAMPLE VIII

    ______________________________________                                         OIL RECOVERY FROM DOG LAKE SAND PACKS                                          ______________________________________                                         Surfactant                                                                             2.0% Petroleum sulfonate + 0.6% sulfo-                                 System: nated 6 mole EO adduct of nonyl phenol                                         + 1% Lignosulfonate in 105,000 ppm TDS                                         brine                                                                  Polymer:                                                                               0.1% Polysaccharide polymer B-1459                                     ______________________________________                                         Carboxy-     % Pore    % Pore                                                  lated        Volume    Volume     % Tertiary                                   Lignosul-    Surfactant                                                                               Polymer    Oil                                          fonate       Injected  Injected   Recovery                                     ______________________________________                                         None         25        100        65.8                                         Norlig 92CAA 25        100        80.0                                         Na salt, softwood                                                              carboxylated with                                                              chloroacetic acid                                                              ______________________________________                                    

EXAMPLE IX

    ______________________________________                                         OIL RECOVERY FROM DOG LAKE SAND PACKS                                          ______________________________________                                         Surfactant                                                                             2.0% Petroleum sulfonate + 0.6% adduct                                 System: sulfonate 6 mole EO adduct of nonyl                                            phenol + 1% Lignosulfonate in 105,000 ppm                                      TDS brine                                                              Polymer:                                                                               0.1% Polysaccharide polymer B-1459                                     ______________________________________                                         Oxidized     % Pore    % Pore                                                  and Carboxy- Volume    Volume     % Tertiary                                   lated Ligno- Surfactant                                                                               Polymer    Oil                                          sulfonate    Injected  Injected   Recovery                                     ______________________________________                                         None         25        100        64.5                                         Norlig 42ZCAA                                                                               25        100        84.1                                         Na salt, Hardwood                                                              oxidized then car-                                                             boxylated with                                                                 chloroacetic acid                                                              ______________________________________                                     

I claim:
 1. In a method for recovering oil from a subteranean formation containing oil and having an injection well and a production well wherein an aqueous surfactant solution is injected into the injection well in order to drive the oil to the production well wherein it is produced the improvement which comprises:injecting into the injection well in admixture with the surfactant lignosulfonates carboxylated with carbon dioxide whereby said carbon dioxide reacts predominantly with the ortho sites of the aryl groups in the lignosulfonates and wherein the lignosulfonate is present in an amount effective for reducing the extent of adsorption of the surfactant by the formation matrix.
 2. A method as in claim 1 wherein the lignosulfonates have a degree of sulfonation ranging from about 2.0 to saturation.
 3. A method as in claim 1 wherein the cation of the lignosulfonate salts is selected from the group consisting of calcium, magnesium, sodium, potassium, and ammonium.
 4. A method as in claim 1 wherein the lignosulfonate salts are present in amount sufficient to occupy substantially all of the active sites on the formation matrix.
 5. A method for recovering oil from a subterranean formation containing oil and having an injection well and a production well comprising:(a) injecting through the injection well into the formation an aqueous solution of lignosulfonates carboxylated with carbon dioxide whereby said carbon dioxide reacts predominantly with the ortho sites of the aryl groups in the lignosulfonates and wherein the lignosulfonate is present in an amount effective for reducing the extent of adsorption of the surfactant by the formation matrix, (b) subsequently injecting into the formation via the injection well an aqueous surfactant solution also containing lignosulfonates carboxylated with carbon dioxide as above and (c) producing oil from the formation via the production well.
 6. A method as in claim 5 wherein the solution step (b) is followed by flooding water.
 7. A method as in claim 5 wherein the lignosulfonates carboxylated with carbon dioxide have a degree of sulfonation ranging from about 2.0 to saturation.
 8. A method for recovering oil from a subterranean formation containing oil and having an injection well and a production well comprising:(a) injecting through the injection well into the formation an aqueous solution of lignosulfonates carboxylated with carbon dioxide whereby said carbon dioxide reacts predominantly with the ortho sites of the aryl groups in the lignosulfonates and wherein the lignosulfonate is present in an amount effective for reducing the extent of adsorption of the surfactant by the formation matrix, (b) subsequently injecting into the formation via the injection well an aqueous surfactant solution and (c) producing oil from the formation via the production well.
 9. A method as in claim 8 wherein the surfactant solution of step (b) is followed by flooding water.
 10. A method as in claim 8 wherein the lignosulfonates have a degree of sulfonation ranging from about 2.0 to saturation. 